The water in swimming pools and spas is constantly re-circulated, and fresh water is normally added only to maintain the desired volume. Although the water is usually filtered continuously to keep it free from suspended matter, it is constantly exposed to infection by pathogenic organisms (bacteria), algae and fungi. Treatment is therefore necessary to control these infections and infestations for reasons of hygiene and appearance.
U.S. Pat. No. 4,014,676 describes the use of poly(hexamethylene biguanide) (PHMB) for controlling algae in swimming pools, and PHMB is commercially available from Avecia, Inc. as a chlorine-free swimming pool sanitizer and algistat under the trademark BAQUACIL. However, while PHMB is a good product for killing pathogenic organisms (a bactericide) in swimming pools and spas at levels of 6–10 ppm, it is generally only algi-static and fungistatic at these levels. Thus the use of PHMB alone to treat swimming pool and spa water will not prevent algal and fungal infestations in the pool.
Swimming pool or spa water can contain a variety of metal ions such as copper, iron and manganese and mineral ions such as calcium. These ions, if present in the water, can reduce the effectiveness of the sanitizer and lead to the development of cosmetically unappealing stains. Chelating agents, such as ethylenediaminetetraacetic acid (EDTA) are often added to water in swimming pools and spas to protect the surfaces and components from being stained by mineral and metal ions and their oxides, hydroxides, carbonates, phosphate, or silicates.
U.S. Pat. No. 5,449,658 discloses that EDTA potentiates PHMB and that a composition comprising EDTA and PHMB provides protection against bacterial, fungal and algal infestations in water. The patent also suggests adding the PHMB and EDTA to the water as a solid or liquid concentrate so as to provide the desired level of PHMB and EDTA in the water. The patent suggests an aqueous concentrate containing from 5–20 weight % PHMB and about 0.5–10 weight % EDTA.
However, we have found that when polymeric biguanides, such as PHMB, are formulated with EDTA in water at the concentrations suggested in U.S. Pat. No. 5,449,648, the resulting formulation is not stable, particularly when the formulation is stored under adverse conditions such as extremes of temperature or extended storage times. We have found that such solutions become cloudy and often form precipitates. The precipitation of the EDTA and/or PHMB from the concentrate results in the incorrect dosage of one or both of these components of the formulation when it is added to the water to be treated, thus reducing the microbiological protection provided by the composition.
There is therefore a need for a stable liquid concentrate of a polymeric biguanide and a chelating agent such as EDTA.